The present invention relates to linear positioning and more specifically to a system which provides both linear and arcuate positioning on a common rail with a very accurate degree of dimensional location. In the early days of linear positioning, carriage and track combinations were utilized for cutting, welding and other machine tool functions but with a minimal degree of positioning accuracy. Typical systems of this nature are illustrated in the following patents: Johnson, et al, U.S. Pat. No. 4,422,384; Appleton, et al, U.S. Pat. No. 3,176,587; Cable, et al, U.S. Pat. No. 3,226,027; Gulley, U.S. Pat. No. Re. 28,121; Livesay U.S. Pat. No. 2,474,153.
The degree of accuracy of the positioning equipment in the patents mentioned above was far less than some design standards of today technology such as required in the field of computer chip integrated circuit design.
Most of the patents above-listed, such as Johnson, et al (U.S. Pat. No. 4,422,384) are concerned with strictly linear movement or strictly non-linear (arcuate) movement with the exception of the patent to Appleton, et al (U.S. Pat. No. 3,176,587). The lastmentioned patent deals with both linear and curved positioning as in the present invention, however, the manner in which it is achieved and the degree of accuracy attained is much different. As shown in FIG. 9 of Appleton, the curved movement is achieved by movement of the spring-biased and tilting trucks 156 and 157. In this less accurate design the distance between the opposing rollers varies in the curved sections while in the present invention, the distance is constant and the curved section is accommodated by selfrotation of the bogie.
The requirements of linear positioning today have substantially changed in the field of microchip integrated circuit design. A critical ingredient is the ability to inscribe even more minute features on a chip. Reductions in circuit size allowing dramatic increases in chip density have taken place in the last few decades and still continue. Today integrated circuit design has run into an obstacle known and referred to as the one micron barrier. One micron is the size of the smallest geometric features on a modern semi-conductor microchips. It is quite difficult to construct chips with feature dimensions below this level. Accurate positioning systems are an essential part of the semi-conductor wafer fabrication, inspection and testing procedures.
In the market today there are a variety of linear positioning systems that provide either strictly linear positioning or strictly non-linear positioning, however, none of them provide guidance in both linear and curved modes while maintaining the accuracy level requirements of current industry. The requirements for linear positioning vary with the engineering application having various accuracy in movement requirements as to horizontal linearity (yaw); vertical linearity (pitch) and lastly roll.
In linear motion applications there is a requirement to restrain the motion of a body in two perpendicular axes while allowing movement in the third. Bearing systems on the market today used for linear positioning involve either a sliding bearing or some type of a rolling bearing.